1. Field of the Invention
The present invention relates to a recording apparatus that records on a recording medium, such as roll paper, by ejecting ink thereon, as well as a recording method for the same. In particular, the present invention relates to a recording apparatus and method capable of recording under little influence of skew of the recording medium.
2. Description of the Related Art
In general, some of image forming apparatuses, in particular, color-image forming apparatuses, are capable of high-volume printing at a time using roll paper to record a plurality of recording sheets. Known examples of this type of recording apparatus that record using roll paper adopt a dry silver-salt system and an inkjet system. A roll of recording medium, such as long recording paper, is generally called roll paper. In the following description, the rolled portion of the roll paper is referred to as a roll, and a sheet-like portion drawn from the roll is referred to as a recording medium.
FIGS. 8A and 8B are diagrams showing a known image forming apparatus; and FIGS. 9A and 9B are plan views showing a conveying mechanism of the known image forming apparatus. The image forming apparatus includes a plurality of recording heads 107 in which nozzle trains are disposed in parallel. A recording medium P drawn from a roll R is conveyed to the recording heads 107 while connected with the roll R. A driving roller 133 that is rotationally driven to generate a conveying force to move the recording medium P in the direction of the arrow (shown) is disposed downstream of the recording heads 107. A conveying roller 131 is disposed upstream of the recording heads 107. The recording medium P having a fixed width is conveyed under a predetermined tension by these rollers 131 and 133. The recording heads 107 eject ink in synchronization with the conveying operations of the rollers 131 and 133 to perform recording.
First, a recording medium P conveying operation will be described from the paper feed side. The recording medium P is held by a feed rotating member 122. The recording medium P is conveyed in the conveying direction by the rotation of the feed rotating member 122. One side edge of the recording medium P held by the feed rotating member 122 is adjacent to a recording-medium reference guide 125 disposed at one widthwise edge perpendicular to the conveying direction. The opposing side edge of the recording medium P is adjacent to a recording-medium moving guide 124 disposed at the other widthwise edge, so that the recording medium P is aligned with respect to the widthwise direction. The recording medium P is conveyed while stretched by a loop detection flag 129 and is introduced in between a reference aligning guide 115 and a moving aligning guide 116 that aligns the widthwise position of the recording medium P. As shown in FIGS. 9A and 9B, the recording medium P is prevented from being conveyed in a direction skewed with respect to the conveying direction using the reference aligning guide 115 and the moving aligning guide 116.
The loop detection flag 129 is provided to swing in the direction of the arrow C. The loop detection flag 129 gives a fixed tension in the conveying direction to the recording medium P. When the recording medium P is conveyed to reduce the amount of loop, the loop detection flag 129 swings. The swing of the loop detection flag 129 is detected by a sensor. A controller rotates the feed rotating member 122 in accordance with the detection signal of the sensor, so that the recording medium P is conveyed toward the aligning guides 115 and 116. As a result, the amount of loop increases, so that the loop detection flag 129 returns to the initial position, and the detection is cancelled; thus, the operation of the feed rotating member 122 is stopped, and the fixed tension of the recording medium P is maintained again. By repeating this operation during the conveying operation, the recording medium P is conveyed, with a stable tension generated on the recording medium P at the upstream side of a conveying roller 131.
The recording medium P, whose one side edge is positioned by the reference aligning guide 115, is conveyed into the nip between the conveying roller 131 and a driven roller 132. The recording medium P is given a fixed conveying force by the conveying roller 131 and the driven roller 132 that rotates following the conveying roller 131 while applying pressure thereto and is conveyed in a recording area at which recording is performed by recording heads 107.
The recording area has the recording heads 107 (107K, 107C, 107M, and 107Y) arranged in the conveying direction, in which a large number of nozzles are arrayed in the direction perpendicular to the conveying direction to spatter the ink. The recording area further has a plurality of upper rollers 134, from the upstream side to the downstream side, for preventing the recording medium P from floating up. The upper rollers 134 decrease the interval between the recording heads 107 and the recording medium P to about 1.00 mm to reduce the displacement of the ink landing positions due to the spattering of the ink, thereby allowing high definition of the image.
The recording medium P on which a high-definition image is formed in the recording area is conveyed by the driving roller 133 and the upper rollers 134 into a cutter area that is a back end process area. The upper rollers 134 are in contact with upper roller cleaners 135 at upper positions, and when coming into contact with the upper surface (recording surface) of the recording medium P, the ink transferred from the recording surface is wiped out by the upper roller cleaners 135. This prevents the ink sticking to the upper rollers 134 from being transferred to the recording medium P when the upper rollers 134 rotate again into contact with the recording surface of the recording medium P. The upper roller cleaners 135 are placed at portions corresponding to the individual upper rollers 134 that are disposed at the region in which the plurality of recording heads 107 are disposed.
The four recording heads 107 shown in FIGS. 8A and 8B are fixed to an elevating head frame 106 and are disposed at positions having a fixed interval from the recording medium P during recording. For storage of the recording apparatus or for a head recovery operation, the elevating head frame 106 is moved to vertically move the recording heads 107. Examples of the structure for the vertical movement include a structure for pulse control using a stepping motor (not shown) and a structure in which the height of the recording heads 107 is held fixed by butting the elevating head frame 106 to a height reference provided in the vertical direction.
In the cutter area, the continuously conveyed recording medium P is stopped during a cutting operation, and after the cutting operation, the recording medium P is conveyed to the next cutting position at a relatively high speed about three times the conveying speed. This operation is repeated, so that the recording medium P is cut to a fixed length in the cutter area. Thus, the recording medium P is conveyed intermittently. The cutter area is therefore provided with a loop region, in which a loop is formed in a portion where the recording medium P is continuously fed to thereby temporarily hold the recording medium P while the recording medium P is stopped during the cutting operation. The cut recording medium P is output from the cutter area, and the series of recording operation is completed.
Although the thus-configured recording apparatuses have generally been used as low-resolution printers for post cards, calling cards, labels, etc. the use for recording high-definition high-quality picture images is considered with the recent remarkable improvement of the inkjet recording system and the material of recording media. In particular, recording apparatuses in which a plurality of long recording heads having nozzle trains having a width equal to the recording width of recording media are disposed in the conveying direction are capable of high-speed recording of about 30 to 100 per minute, thus having a tendency to increase in demand.
The technology for conveying a recording medium on the conveying path, with the side edges of the recording medium positioned, is disclosed in Japanese Patent Laid-Open No. 08-133540.
However, with the above-described configuration, if the angle of the reference aligning guide 115 with respect to the nip between the conveying roller 131 and the driven roller 132 is not a right angle with high accuracy, the skew of the recording medium P occurs at the beginning of the feeding operation. If the recording medium P skewed with respect to the conveying direction is fed to the conveying roller 131, the conveying roller 131 conveys the recording medium P in the direction of the skew, so that the recording medium P is continuously skewed. However, the skew is corrected owing to the influence of a tension generated in the recording medium P between the feed rotating member 122 and the conveying roller 131, and is gradually settled. However, if the conveying force at the nip is strong, the skew of the recording medium P is not settled, so that the recording medium P is continuously skewed, causing a paper jam.
To convey the recording medium P smoothly, a slight gap is needed between both widthwise edges of the recording medium P and the guides 115 and 116. The side edge faces of the roll R are not sometimes flat due to an error of the width of the recording medium P to cause deviation of the positions of the side edges between the vicinity of the outer circumference and the vicinity of the center. Therefore, gaps are needed between the recording medium P and the guides 115 and 116. Thus, even after the skew at the beginning of the feeding operation is settled during a conveying operation, as described above, the conveyed recording medium P is skewed at a low frequency due to the gaps.
The skew generated at the low frequency is caused by the gaps that are necessary to convey the recording medium P, described above. However, to reduce the conveying resistance of the recording medium P, these gaps should not be eliminated. Therefore, to reduce the skew at the beginning of the feeding operation, various configurations are proposed for bringing the widthwise direction of the recording medium P perpendicular to the conveying direction using a skewing roller that conveys the recording medium P in a direction skewed from the conveying direction.
In particular, high-quality printing using a plurality of long inkjet recording heads is affected by even high-frequency skew generated after the first skew is settled. Therefore, the configuration using a plurality of long recording heads has the problem that the skew induces the displacement of ink landing positions among the parallel nozzle trains, so that high-quality images cannot be formed.
To constitute the nozzle trains of the recording heads at relatively low cost, there is also a configuration in which a plurality of chips each having relatively short nozzle trains are arranged in the column direction to constitute long recording heads. However, this configuration is required to reduce the skew more because when the recording medium is skewed, a phenomenon in which the gaps between the individual chips change to generate alternate white and black stripes on the recording surface of the recording medium is caused depending on the amount of skew. In general, the amount of widthwise displacement of the recording medium p when the recording medium P is skewed must be held within ±20 μm or less, which is difficult to achieve with the present configuration of the conveying mechanism.